Recently, the reservoir characteristics and well structures in oil and gas well drilling become more and more complex, and oil and gas kick accidents happen frequently, resulting in increase of non-operation time and drilling cost in well drilling. After kick happens in a well, the formation fluids (oil, gas, and water) may invade into the wellbore, be mixed with the drilling fluid and migrate along the wellbore. If the kick fluid is a gas, subjecting to the influence on the environment change on pressure and temperature, it may have severe phase transition, rise and expansion in the migration process, bringing a serious challenge to wellbore pressure control. Therefore, it is very important to identify and diagnose kick information timely, to ensure safe and efficient well drilling.
The invasion of formation fluids may result in change of flow behaviors and physical parameters of the fluid in the wellbore. Based on that fact, existing kick detection techniques have been developed, and these kick detection techniques can be categorized into: diagnostic methods based on flow measurement, including drilling fluid pit increment method, outlet flow difference method, and downhole micro-flow measurement method, etc.; diagnostic method based on pressure and temperature measurement, including Annulus Pressure While Drilling (APWD), Logging While Drilling (LWD), and Rapid Annulus Temperature (RAT), etc.; diagnostic methods based on measurement of gas void fraction in fluid, including acoustic measurement method, resistivity measurement method, and natural gamma monitoring method (LWD), etc.
To avoid gas over-expansion and control the wellbore pressure timely, diagnostic methods based on downhole measurement techniques were the main development direction of kick detection in the early stage. However, the applicability and time efficiency of those methods are quite limited in the kick detection in horizontal wells. Firstly, since gas doesn't expand when it migrates in a horizontal section, the flow and pressure variations are not apparent, and it is difficult to measure directly to realize early identification. Secondly, since a risk of formation fluid invasion exists at all positions in a horizontal section, it is unable to judge the kick information above the bottom hole based on the measurement data obtained at the bottom hole. Finally, since the pressure variations are not apparent, it is difficult to judge the kick information, etc timely. However, the identification of kick fluid type, kick rate, and kick occurrence position has important meaning in understanding about the formation characteristics, judging the causes for kick, and conducting follow-up wellbore pressure control.
To overcome the drawbacks in the prior art, the present invention provides a measuring unit, a kick information identification apparatus and method, which are applicable to kick information identification in horizontal wells.